The present disclosure relates to fixing devices and image forming apparatuses such as copiers and printers equipped with the fixing device, and in particular, relates to improvements in the heat insulating properties of the fixing devices.
An image forming apparatus includes a charger unit, an image carrying body (photoconductor drum), an exposure unit, a developing unit, a transfer unit, and a fixing device. The fixing device causes a toner image to be fixed onto a recording medium by heating and pressing unfixed toner.
In the fixing device described above, the heat not used in the fixing operation is released outside of the fixing device. Thus, unnecessary heat is transferred to a photoreceptor and a cleaning unit, which are located around the fixing device. As a result, the drive torque of the apparatus is increased due to compression of the toner. Operation of the apparatus may be stopped or an abnormal density observed due to non-uniform charge on the surface of the photoreceptor. Furthermore, since the heat released from the fixing device increases the inner temperature of the apparatus, other systems inside the apparatus may be adversely affected, thereby the image quality and durability of components may be degraded.
Measures such as suppressing temperature rise by providing airflows between the fixing device and other systems have been used. However, cooling the fixing device results in an increase in unnecessary energy consumption due to an increase in the amount of heat generation for ensuring the necessary amount of heat required for a fixing operation.
In view of the above-described situation, a method has been proposed, in which heat release from the fixing device is suppressed without using a cooling unit such as a fan. For example, there is a technology in which, in a heat-roller type fixing device, heat released from a fixing roller is suppressed by positioning around the fixing roller a heat insulating material that blocks heat released from the fixing roller and by forming a heat insulating air layer between the inner circumferential surface of the heat insulating material and the outer circumferential surface of the fixing roller. Also, in a fixing device, a heat insulating material is located on the inner wall surfaces of the upper and lower covers of the fixing unit, the upper and lower covers opposing a fixing roller and a pressure roller.
From the viewpoint of energy savings, a reduction in stabilization time for fixing and reduction in energy consumption are important. For these tasks, diameters and thicknesses of fixing rollers have been reduced so as to improve temperature rise characteristics of the fixing rollers.
However, when rollers having a small thickness are used as the fixing rollers, the fixing rollers have a small heat capacity. Thus, it is difficult to effectively suppress heat release from the fixing rollers even when heat insulating materials are provided.